Double fisherman's knot


The double fisherman's knot or grapevine knot is a bend. This knot and the triple fisherman's knot are the variations used most often in climbing, arboriculture, and search and rescue. The knot is formed by tying a double overhand knot, in its strangle knot form, with each end around the opposite line's standing part.

Usage

A primary use of this knot is to form high strength slings of cord for connecting pieces of a climber's protection system.

Other uses

This knot, along with the basic fisherman's knot can be used to join the ends of a necklace cord. The two strangle knots are left separated, and in this way the length of the necklace can be adjusted without breaking or untying the strand.

Tying

Line form

Drop form

Security

A study of 8 different bends using climbing ropes concluded "the Double Fisherman's Knot seemed to be the best joining knot". The butterfly bend held under slightly more weight, but "almost impossible to untie after a significant load of about 1,000 lb was applied".
Dyneema/Spectra's very high lubricity leads to poor knot-holding ability and has led to the recommendation to use the triple fisherman's knot rather than the traditional double fisherman's knot in 6 mm Dyneema core cord to avoid a particular failure mechanism of the double fisherman's, where first the sheath fails at the knot, then the core slips through.